The present invention provides a microcontroller-based system for detecting ground-fault and grounded-neutral conditions in a monitored circuit of an electrical power distribution system having both line and neutral conductors. The system includes a sensor producing an output signal responsive to current flow in both the line and neutral conductors of the monitored circuit. The system also includes a microcontroller for receiving and evaluating the sensor output signal and initiating a circuit status signal indicating whether the monitored circuit is operating normally, has a ground-fault condition or a grounded-neutral condition. The microcontroller analyzes the sensor output signal with respect to predetermined or calculated parameters to determine if a ground-fault condition is present in the monitored circuit. At selected intervals the microcontroller initiates a pulse, referred to herein as a ping, in a resonant circuit of the sensor and analyzes the sensor's response to the ping to determine if a grounded neutral condition exists in the monitored circuit.